Adjustable sliding brush transformer



Dec. 8, 1964 Filed Aug. 9, 1961 J. P- STEFANI ETAL ADJUSTABLE SLIDING BRUSH TRANSFORMER 2 Sheets-Sheet l [n @1276; dbsep/z P51212226 Brim? 1Q Rem/2, PF)?!" L. 50/40 fi GM/R 7:42;? 7/?6/7" fifomgy.

1964 J. P. STEFAN! ETAL 3,160,841

ADJUSTABLE SLIDING BRUSH TRANSFORMER 2 Sheets-Sheet 2 Filed Aug. 9, 1961 United States Patent 3,16%,841 ADJUSTABLE SLlDlNG BRUSH TRANSFORMER Joseph P. Steiani, Richard A. Rawson, and Peter L. Soldato, Pittsficld, Mesa, assignors to General Electric Company a corporation or New York Filed Aug. 9, 1961, Ser. No. 13%,365 9 Claims. (Cl. 336-137) This invention relates to adjustable sliding brush transformers, and more in particular to improved means for conducting current from the brush of the transformer to a fixed terminal connectable to an external circuit.

Some adjustable sliding brush autotransformers employ a rotatable brush that moves along the commutator surface of the autotransformer winding. Such autotransformers also may employ a fixed terminal for connection to an external circuit. Problems are encountered in conducting current from the sliding brush to the fixed terminal in that the conducting means must be operable for the various positions of the brush along the winding commutator surface.

Numerous arrangements have been proposed by the prior art for conducting current from the brush to the fixed terminal. For example in one prior art arrang ment the brush has been connected to a rotatable metal ring that is in sliding contact with a lever spring which is electrically connected to the fixed terminal. This arrangement has the disadvantage that in time the lever spring becomes weakened, thus causing the electrical contact it makes with the metal ring to vary; reduced contact pressure causes arcing and eventual failure of the contact surfaces. The life of the lever spring is reduced because the spring is employed to conduct current; this heats the spring and accelerates its loss in strength.

In some prior art arrangements of the above described type, the brush and other current conducting elements are mounted on a radiator member of the autotransformer and the current is conducted through the radiator member. The radiator members have a relatively poor electrical conductivity, so the PR losses: caused by the current passing through them are appreciable. This decreases the heat transfer efficiency of the radiator members by increasing their temperature.

Another prior art arrangement is to employ a circular rotating terminal on one end of a shaft, with the rotating terminal being engaged by a stationary finger connected to the stationary external terminal. The other end of the shaft contains an arm carrying the brush which slides along the autotransformcr winding. Current is conducted from the brush through the arm, then through the shaft to the rotating terminal, and finally through the fixed finger to the external terminal. This arrangement is undesirable in that the path through which the current is conducted is very long; this causes unnecessary electrical losses and heating in the apparatus because the shaft, brush supporting arm, and contact members cannot always be made from electrically highly conductive materials. Furthermore, having the brush at one end of the shaft and the rotating contact at the other end increases the difficulty of inspection of the apparatus in that one end of the autotransiormer is normally afiixed to some supporting surface.

Other arrangements for conducting current from the rotating brush to a fixed contact require the use of wires wrapped around a rotating shaft. These arrangements are undesirable in that the wire is flexed or unwound during rotation of the brush, and eventually this causes breaking of the wire.

Accordingly it is an object of our invention to provide improved means for conducting current from the rotating brush or" an adjustable autotransformer to a fixed terminal 3,150,841 Patented Dec. 8, 1964 that does not have the disadvantages of prior art arrangements.

A broader object of the invention is to provide an improved sliding brush transformer.

Another object of the invention is to provide improved means for conducting current from the rotating brush of an autotransformer to a fixed terminal that does not require the use of lever springs.

A further object is to provide improved means for electrically connecting the sliding brush of an autotransformer to a fixed terminal in which the means for supporting the sliding brush is in continuous electrical contact with a current collector for the terminal.

Another object is to provide an improved arrangement for conducting current from the sliding brush of an autotransformer that is mounted on a radiator member in which current passing between the brush and a fixed terminal does not pass through the radiator member so as to decrease its heat transfer efficiency by causing heating thereof.

Another object is to provide an arrangement for conducting current irom the sliding brush of an autotransformer to a fixed terminal that is economical and requires a minimum number of parts.

Another object is to provide an improved arrangement for conducting the current from the sliding brush of an autotranstormer to a fixed terminal that facilitates inspection of commutator surfaces and replacement of worn or damaged parts.

Another object is to provide improved means for conducting current from a sliding brush of an autotransformer to a fixed terminal that does not have commutator surfaces that readily collect dust or other contaminants.

Another object of the invention is to provide improved means for conducting current from the sliding brush of an autotransformer to a fixed terminal in which the commutator surface of the brush and the commutator surface of the conducting means are at the same end of the autotransformer.

Other objects and advantages of the invention will become apparent from the specification, drawing, and claims, and the scope of the invention will be pointed out in the claims.

Briefly stated, according to one aspect of our invention, a sliding brush autotransformer may have its brush mounted on a rotatable, circular radiator member so that movement of the brush along the autotransformer winding is achieved by rotation of the radiator member. We provide improved means for conducting current from the brush to a fixed terminal which is connectable to an external load circuit. The current conducting means comprises a layer of electrically highly conductive material on the external circumferential edge of the radiator member. The layer is connected to the brush, and a current collecting contact is resiliently urged into sliding electrical contact with the layer for the various positions of the brush along the winding. The circuit between the brush and the fixed terminal is completed by electrical connection of the contact to the fixed terminal.

In the drawing:

FTGURE 1 is a schematic, isometric, partially broken away view of a sliding brush autotransformer in accord with the teachings of our invention.

FIGURE 2 is a partially broken away top plan view of the autotransformer shown in FIGURE 1.

FIGURE 3 is a cross-sectional view taken along the line 3-3 in FIGURE 2.

Turning now to the drawing, therein is shown an embodiment of an electrical sliding brush autotransformer It? in accord with the teachings of our invention. The autotransformer ltd has'an annular magnetic core 11 surrounded by insulation 12, over which an insulated conductor is coiled to provide a toroidal winding 13. The winding 13 is provided with a commutator surface 14-, as for example by removing insulation from adjacent turns of the Winding by grinding the turns fiat. A high resistance brush 15 of graphite or carbon material slides over the commutator surface 14 in electrical contact therewith to provide an autotransformer connection. The ends of the winding 13 are connectable by means of leads 16 and 17 to a suitable input source of alternating current E. The output of the autotransformer may be obtained by connection of one output terminal 18 to one of the input leads 16 and connection of the other output terminal 19 to the brush 15 in the manner described in paragraphs that follow. An external load 20 may be connected across the output terminals 18 and 19. The autotransformer is supported on a suitable base member 21, which may have a terminal board 22 attached thereto. The winding 13 does not completely encompass the core in that its ends terminate short of each other to provide a space at 23. This enables the terminal board 22 and a contact thereon (described hereafter) to be located adjacent the space 23 and thus not interfere with travel of the brush over active winding turns.

The brush 15 is mounted in any convenient manner on a radiator member 25 that dissipates to the atmosphere heat generated by the brush and other components of the auto-transformer. The radiator member 25 may be fabricated by casting a metal having relatively low electrical conductivity. The radiator member 25 is attached to a shaft 26, which is rotatably journaled in the base member 21. A knob 27 of insulating material may be afiixed to the shaft 26 to facilitate manual positioning of the brush 15 in the desired location on the commutator surface 14. A coil spring 29 may be employed to maintain a desired electrical contact presure between the brush 15 and surface 14.

Electrical connection between the sliding brush 15 and the fixed output terminal 19 is obtained by electrically connecting the brush, as for example by means of a lead 28, to a layer (it) of electrically highly conductive material on the external circumferential edge or rim of the radiator member 25. The exterior surface of the layer 30 continually touches and makes sliding electrical contact with a stationary current collecting contact 31. The contact 31 may be a brush made of copper-graphite, silver-graphite, or some other similar low resistance, low friction material; the brush may be housed in an opening 32 in the terminal board 22. The current collecting contact 31 is resiliently urged into contact with the layer 30 by a coil spring 33. The layer contact 31, and spring 33 all lie in a plane substantially perpendicular to the central axis 34 of the winding 13 so that the spring 33 produces a force that acts in the plane of these elements; this arrangement produces a relatively high, controllable electrical contact pressure between the layer 3% and contact 31, and prevents the loss of contact pressure inherent in lever spring arrangements. The exterior surface of the layer 319 is substantially parallel to the winding central axis 34. Thus when the base 21 is supported on a horizontal surface, the exterior surface of the layer 30 will be vertical and will not readily collect dust or other contaminating substances. The contact 31 is electrically connected to the fixed terminal 19 by suitable means such as a lead 35, so that the spring 33 need not carry current. The contact 31 and terminal board 22 are located radially opposite the space 23 so as not to interfere with travel of the brush 15 along the communtator surface 14.

The highly conductive layer 3% may be formed by pro viding a groove 46 in the external circumferential edge or rim of the radiator member 25, and placing a ring 4 1 of electrically high conductive material in the groove. As shown in FIG. 2, the ends 4?. and 43 of the ring 41 may terminate short of each other to provide a space therebetween for mounting the brush 15 on the radiator member 25. If desired, suitable means, such as screws (not illustrated), may be employed for fastening the ring 41 in the groove 4%. The radiator member 25 may be painted or otherwise coated so as to be electrically insulated from the ring 41 to prevent current from being conducted through the radiator member. This prevents heating of the radiator member caused by PR losses, and thus increases its heat transfer efliciency.

Aluminum, copper, silver, and yellow brass are examples of metals suitable for use as the layer 39. Combinations of the above metals may be employed, as well as laminated materials, as for example yellow brass coated with silver. For example, the. ring 41 may be of yellow brass while the highly conductive layer 30 may be a coating of silver on the exterior surface of the yellow brass. The last-mentioned coated material has the advantage that relatively inexpensive yellow brass is employed as w the base material, yet the advantages of highly oxidation-resistant silver on the exterior surface are obtained. An alternative arrangement would be to omit the groove it) but coat the circumferential edge of the radiator 25 with a highly conductive material, as by spraying, plating, or other methods, instead of employing the ring 4-1 in the groove 4%}. Thus it will be apparent that the high ly conductive layer 39 may be a ring 41 of highly conductive material, it may be a layer coated on a ring member, or it may be a layer coated directly on the circumferential edge of the radiator.

It has thus been shown that by the practice of our invention electrical contact may be maintained between the sliding brush 15 of an autotransformer and a fixed terminal 19 through the use of the external circumference or rim of a radiator member 25 on which the brush is mounted. Thus the heat transfer efficiency of the radiator member isnot decreased by PR losses caused by current passing therethrough. Our arrangement also reduces the number of parts required and eliminates the diiiiculties previously encountered with lever spring arrangements. Locating of the autotransformer commutator surface 14 and the commutator-like exterior surface of the layer 3d at the same end of the autotransformer, with both surfaces being easily accessible and visible from the outside of the apparatus, facilitates inspection, repair, and replacement of worn or damaged elements, such as the springs 29 and 3?). Furthermore, the electrical contact surface of the layer 30 is not in a horizontal plane, so dust and other contaminants do not readily adhere thereto.

It will be understood, of course, that While the form of the invention herein shown and described constitutes a preferred embodiment of the invention, it is not intended herein to illustrate all of the equivalent forms or ramifications thereof. For example, although the ring 41 has been illustrated as housed in the groove 4t), those skilled in the art will realize that the groove 40 could be omitted, and the ring 41 attached to the exterior rim of the radiator member 25. It will also be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed, and it is aimed in the appended claims to cover all such changes as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a sliding brush transformer of the type having its brush mounted on the periphery of a circular radiator member, whereby movement of the brush along the transformer winding is achieved by rotation of the radiator member about a central axis perpendicular to said memher, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external circuit comprising, a layer of electrically highly conductive material on the external circumferential edge of said radiator member electrically connected to said brush, a current collecting contact resiliently urged into sliding electrical contact with said layer, and said current collecting contact being electrically connected to said fixed terminal.

2. In a sliding brush transformer of the type having its brush mounted on a rotatable circular radiator member, whereby movement of the brush along the Winding is achieved by rotation of the radiator member about a central axis perpendicular to said member, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external circuit comprising, a ring of electrically highly conductive material housed in a groove provided in the external circumferential edge of said radiator member, said ring being electrically connected to said brush, a current collecting contact resiliently urged into sliding electrical contact with said ring, and said current collecting contact being electrically connected to said fixed terminal.

3. In a sliding brush autotransformer of the type having its brush mounted on a rotatable circular radiator member, whereby movement of the brush along the winding is achieved by rotation of the radiator member about a central axis perpendicular to said member, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external load comprising, a split ring of electrically high conductive material housed in a groove provided in the external circumferential edge of said radiator member, the ends of said ring terminating short of each other to provide space for mounting said brush therebetween, said ring being electrically connected to said brush, a current collecting contact resiliently urged into sliding electrical contact with said ring, and said current collecting contact being electrically connected to said fixed terminal.

4. In a sliding brush autotransformer of the type having its brush mounted on a rotatable circular radiator member, whereby movement of the brush along the autotransformer winding is achieved by rotation of the radiator member about a central axis perpendicular to said member, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external load comprising, a layer of electrically highly conductive material on the external circumferential edge of said radiator member, said layer lying in a plane substantially perpendicular to the central axis of said winding, said layer being electrically connected to said brush, a current collecting contact, spring means producing a force acting in said plane to resiliently urge said current collecting contact into sliding electrical contact with said layer for the various positions of said brush along said winding, and said current collecting contact being elec trically connected to said fixed terminal.

5. In a sliding brush autotransformer of the type having its brush mounted on a circular radiator member attached to a perpendicularly extending center shaft which is rotatably journaled in a base member supporting said autotransformer, whereby movement of the brush along the autotransformer winding is achieved through rotation of the radiator member by rotation of said shaft, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external load comprising, a layer of electrically highly conductive material on the external circumferential rim of said radiator member electrically connected to said brush, a terminal board including said external terminal supported by said base member, a current collecting contact mounted on said terminal board, said contact being spring-urged into sliding electrical contact with said layer for the various positions of said brush along said winding, and said contact being electrically connected to said fixed terminal.

6. In a sliding brush transformer of the type having its brush mounted on a rotatable circular member having relatively low electrical conductivity, whereby movement of the brush along the autotransformer winding is achieved by rotation of the circular member about a central axis perpendicular to said member, the improvement in means for conducting current from the brush to a fixed terminal connectable to an external circuit comprising a layer of electrically highly conductive material on the external circumferential edge of said circular member, said layer lying in a plane substantially perpendicular to the central axis of said winding, said layer being electrically connected to said brush, a current collecting contact, a coil spring producing a force acting in said plane to resiliently urge said contact into sliding electrical contact with said layer for the various positions of said brush along said Winding, and said contact being electrically connected to said fixed terminal.

7. An adjustable autotransformer comprising a base member supporting a toroidal winding coiled around an annular core, a rotatable shaft extending axially through the center of said core, a circular metal radiator member having relatively low electrical conductivity affixed at its center perpendicular to said shaft so as to be rotatable therewith, a high resistance brush slidable along a commutator surface on said winding, said brush being mounted on said radiator member whereby sliding movement of the brush along the winding commutator surface is achieved by rotation of the radiator member, a fixed terminal connectable to an external load, means for conducting current from the sliding brush to the fixed terminal comprising a ring of electrically highly conductive metal in a groove provided in the external circumferential rim of said radiator member, said ring being located in a plane substantially perpendicular to the central axis of said Winding, the exterior surface of said ring being electrically connected to said brush, a terminal board including said fixed terminal supported by said base member, a current collecting contact mounted in an opening in said terminal board, a coil spring in said opening producing a force acting in said plane to resiliently urge said current collecting contact into sliding electrical contact with the exterior surf-ace of said ring for the various positions of said brush along the commutating surface of the Winding, and said current collecting contact being electrically connected to said fixed terminal.

8. An adjustable autotransforrner comprising a base member supporting a toroidal winding coiled around an annular core, a rotatable shaft extending axially through the center of said core, a circular metal radiator member having relatively low electrical conductivity afiixed at its center to said shaft so as to be rotatable therewith in a plane perpendicular thereto, a high resistance brush slidable along a commutator surface on said Winding, said brush being mounted on said radiator member whereby sliding movement of the brush along the winding commutator surface is achieved :by rotation of the radiator member, a fixed terminal connectable to an external load, means for conducting current from the sliding brush to the fixed terminal comprising a split ring of electrically highly conductive metal in a groove provided in the external circumferential edge of said radiatior member, said ring being located in a plane substantially perpendicular to the central axis of said Winding with the exterior surface of said ring being substantially parallel to said central axis, the ends of said ring terminating short of each other so as to provide space for mounting said brush therebetween, the

exterior surface of said ring being electrically connected to said brush, a terminal board including said fixed terminal supported by said base member, a current collecting contact mounted in an opening in said terminal board, a coil spring in said opening producing a force acting in said plane to resiliently urge said current collecting contact into sliding electrical contact with the exterior surface of said ring for the various positions of said brush along the commutating surface of the winding, and said current collecting contact being electrically connected to said fixed terminal.

9. An adjustable transformer comprising an annular core, a toroidal Winding encompassing said core except for a space Where the ends of the winding terminate short of each other, a base member supporting said core and Winding, a rotatable shaft extending axially through the center of said core, a circular metal radiator memher having relatively low electrical conductivity affixed at its center to said shaft so as to be rotatable therewith in a plane perpendicular thereto, a high resistance brush slidable along a commutator surface on said winding, said brush being mounted on said radiator member whereby sliding movement of the brush along the Winding commutator surface is achieved by rotation of the radiator member, a fixed terminal connectable to an external circuit, means for conducting current from the sliding brush to the fixed terminal comprising a ring of electrically highly conductive metal in a groove provided in the external circumferential edge of said radiator member, said ring being located in a plane substantially perpendicular to the central axis of said winding with the exterior surface of said ring being substantially parallel to said central axis, the exterior surface of said ring being electrically connected to said brush, a terminal board including said fixed terminal supported by said base member, a current collecting contact mounted in an opening in said terminal board, a coil spring in said opening producing a force acting in said plane to resiliently urge said current collecting contact into sliding electrical contact with the exterior surface of said ring for the various positions of said brush along the commutating surface of the Winding, said current collecting contact being electrically connected to said fixed terminal, and said terminal board and current collecting contact being located adjacent said space Where the ends of the Winding terminate short of each other so as to prevent interference with travel of said brush over the Winding.

i-lenniker Mar. 1, 1949 Snowdon Mar. 21, 1961 

1. IN A SLIDING BRUSH TRANSFORMER OF THE TYPE HAVING ITS BRUSH MOUNTED ON THE PERIPHERY OF A CIRCULAR RADIATOR MEMBER, WHEREBY MOVEMENT OF THE BRUSH ALONG THE TRANSFORMER WINDING IS ACHIEVED BY ROTATION OF THE RADIATOR MEMBER ABOUT A CENTRAL AXIS PERPENDICULAR TO SAID MEMBER, THE IMPROVEMENT IN MEANS FOR CONDUCTING CURRENT FROM THE BRUSH TO A FIXED TERMINAL CONNECTABLE TO AN EXTERNAL CIRCUIT COMPRISING, A LAYER OF ELECTRICALLY HIGHLY CONDUCTIVE MATERIAL ON THE EXTERNAL CIRCUMFERENTIAL EDGE OF SAID RADIATOR MEMBER ELECTRICALLY CONNECTED TO SAID BRUSH, A CURRENT COLLECTING CONTACT RESILIENTLY URGED INTO SLIDING ELECTRICAL CONTACT WITH SAID LAYER, AND SAID CURRENT COLLECTING CONTACT BEING ELECTRICALLY CONNECTED TO SAID FIXED TERMINAL. 